docs: def remove(self, symbol):
          """
          Remove the entry for the unit matching `symbol`.
  
          Parameters
          ----------
  
          symbol : str
             The name of the unit symbol to remove from the registry.
  
          """
          self._unit_system_id = None
  
          if symbol not in self.lut:
              raise SymbolNotFoundError(
                  "Tried to remove the symbol '%s', but it does not exist "
                  "in this registry." % symbol
              )
  
          del self.lut[symbol]